Process for the silylation of inorganic oxides

ABSTRACT

The invention relates to a process for the silylation of very finely divided inorganic oxides, in which the very finely divided inorganic oxides are treated with at least one silylating agent which is relatively nonvolatile in the temperature range of the overall process, with the proviso that the relatively nonvolatile silylating agent is admixed with the very finely divided inorganic oxides as a liquid, in the form of a very finely atomized aerosol. Furthermore, the invention relates to a highly apolar, pyrogenic silica prepared by this process.

FIELD OF THE INVENTION

The present invention relates to highly apolar inorganic oxides such assilica, to a process for the preparation of highly apolar inorganicoxides and to their use.

BACKGROUND OF INVENTION

The use of inorganic oxides, for example silica, as thickeners andthixotropic agents in liquids is known. The thickening and thixotropiceffect can be explained by the establishment of a three-dimensionalnetwork of silica particles within the liquid. For the development andstability of the network in the liquid, it is the interactions betweenthe silanol groups of neighboring silica particles, for example via theformation of hydrogen bonds, which are critical. In apolar liquids theseinteractions have their full effect. The action of silica as a thickenerof liquids is therefore particularly well pronounced in apolar systemsor systems of low polarity, such as hydrocarbons orpolydimethylsiloxanes. In media having a high affinity for the silanolgroups of the silica surface, for example via hydrogen bonds,destabilization of the three-dimensional silica network occurs. For thisreason, the thickening of highly polar liquids such as water or ethanolis only possible with large quantities of silica. Polar systems such assolvents, polymers or resins which comprise oxygen-containing polargroups, for example keto, epoxy, ether, ester, hydroxyl or carboxylgroups, or nitrogen-containing polar groups, for example primary,secondary or tertiary amino, amido, imino groups or quaternary ammoniumgroups, are of great industrial importance--examples being epoxy resins,polyurethanes, vinyl ester resins or aqueous dispersions andemulsions--as paints, coating compositions or adhesives. In order tosuppress the destabilizing effect of the silanol groups of the silicasurface on the development of the three-dimensional particle network,attempts are made to thicken such systems and to render them thixotropicusing apolar silicas, i.e., those silicas whose content of surfacesilanol groups is reduced. However, the success of such attempts ishighly variable and appears to be dependent on the system.

One object of the present invention is the effective elimination of thesilanol groups on the silica surface, that is, the complete silylationof the silica, since these silanol groups in polar systems, destabilizethe three-dimensional particle network which is necessary for thickeningand thixotropy.

Processes for the preparation of apolar silicas are known.

DE-B 11 63 784 (Deutsche Gold- und Silber- Scheideanstalt) and DE 32 11431 (Degussa AG), disclose processes for the silylation of silica. Inthe processes described in these documents, silica which has silanolgroups on its surface is dried in a dry stream of inert gas attemperatures of from 600° C. to 1000° C., preferably from 800° C. to900° C., to give an absolutely dry product and is silylated withsilylating agents such as alkyl- or aryl- or mixedalkyl-aryl-halosilanes. In this process the silica is treated in theabsence of oxygen with small quantities of steam, with an inert gas andwith a gaseous silylating agent at a temperature from 200° C. to 800°C., preferably at from 400° C. to 600° C. A disadvantage of this processis the low yield of silica-bonded silylating agent. A furtherdisadvantage of this process is the residual content of surface silanolgroups of the silica.

DE-A 19 16 360 (Deutsche Gold- und Silber- Scheideanstalt) describes aprocess in which silica is dried in a fluidized bed with a dry stream ofinert gas at temperatures of from 600° C. to 1000° C., preferably from800° C. to 900° C., to give an absolutely dry product which is loaded attemperatures of from 25° C. to 350° C. with linear and/or cyclicorganopolysiloxanes and, if desired, organohalosilanes, which have beenconverted into the gas phase, and is reacted at temperatures in therange from 350° C. to 650° C. with organosilicon compounds, before beingtreated at temperatures of from 125° C. to 500° C. The silylating agentsused are linear or cyclic organopolysiloxanes which can be vaporized inthe temperature range mentioned or are formed as vapor in thistemperature range, or mixtures.

The processes described above operate with gaseous silylating agents.The actual chemical reaction of silylation is therefore subsequent tothe equilibrium of adsorption/ desorption between gaseous andsurface-bound silylating agent. At the elevated temperatures which arenecessary for the chemical fixation of the silylating agent, thisequilibrium lies heavily on the side of desorption of the silylatingagent from the silica surface. Consequently the yields which can beobtained, based on silylating agent employed to silylating agent bondedto silica, are low. The low yield leads to increased environmentalpollution owing to unreacted silylating agent, and to high costs.

DE-A 25 13 608 (Deutsche Gold- und Silber- Scheideanstalt) discloses aprocess in which silica is dried in a fluidized bed with a dry stream ofinert gas at temperatures of from 600° C. to 1000° C., preferably from800° C. to 900° C., to give an absolutely dry product which issubsequently brought into a fluidized state while heating attemperatures in the range from about 200° C. to 300° C., during which itis admixed dropwise with a volatile organosilane which is stable andboils at below 300° C. Laboratory experiments indicate, however, thatthe dropwise addition of organosilane to silica at temperatures abovethe boiling point of the silane gives a poor yield and, does not lead tothe high degrees of silylation desired.

DE-A 24 03 783 (Bayer AG) describes a process for the silylation ofsilica, in which silica is sprayed over the fluidized silica with amixture of a liquid organosilane which reacts slowly with water, andlarge quantities of water, which are about 50% above those of thesilazane used, at temperatures of from 0° C. to 100° C., preferably roomtemperature, and the resulting product is freed from the volatileconstituents at temperatures of from 130° C. to 170° C. As describedtherein, the thickening effect of the resulting silica is severelyreduced by the treatment.

In DE 27 28 490 (Deutsche Gold- und Silber- Scheideanstalt), silica issilylated using organopolysiloxanes in appropriate solvents. The silicaformed exhibits neither substantial thickening nor structuring ofliquids.

In addition, processes are known in which pulverulent inorganic oxides,for example silicas, are sprayed with liquid organosilicon compounds inthe form of small, liquid drops. Very finely divided inorganic oxides,such as highly disperse silicas, are characterized by extremely lowprimary particle diameters, within the submicron range. Spraying with asilylating agent by conventional spraying techniques has been found tolead to inhomogeneous covering and to particles which are onlyphysically coated and which are not completely apolar. Our laboratoryexperiments show that such processes are unsuitable for the homogeneouscovering of highly disperse silicas with the development of a highdegree of silylation and the elimination of all reactive silanol groups,and with a coat of silylating agent which is fixed completelychemically, i.e., which is no longer soluble. These problems occur inparticular when using silylating agents of high viscosity.

In DE 21 070 82 (Imperial Chemical Industries Ltd.), pyrogenic silica issprayed with liquid organosilicon compounds. However, only a moderatedegree of silylation of the silica is achieved, characterized by amethanol number (defined therein as the percentage by weight of methanolin water which is sufficient to wet the silica completely, to bringabout complete sinking of the silica in a water/methanol mixture) ofless than 35.

In the process according to DE 20 57 731 (Deutsche Gold- undSilber-Scheideanstalt) it is necessary to add ammonia in order to rendersilica hydrophobic when it is sprayed with alkoxysilanes and/oralkoxy-terminal organosiloxanes.

DE-A 37 07 226 (Wacker-Chemie GmbH) discloses a process for thepreparation of highly disperse metal oxide having a surface modified byammonium-functional organopolysiloxane, as a charge controlling agentfor positive chargeable toners, in which an alcoholic solution of anammonium-functional organopolysiloxane is added to the silicon dioxide.

A disadvantage of the prior art is that complete silylation of thesilica while retaining its thickening effect, does not occur, althoughlarge excess quantities of silylating agent are employed, which therebyrepresent pollution to the environment.

SUMMARY OF INVENTION

The object of the present invention is to improve the known silylationprocesses and to provide a highly apolar silica having improvedproperties. This object is achieved by the invention.

The present invention relates to a process for the silylation of veryfinely divided inorganic oxides, characterized in that the very finelydivided inorganic oxides are treated with at least one silylating agentwhich is relatively nonvolatile in the temperature range of the overallprocess, with the proviso that the relatively nonvolatile silylatingagent is admixed as a liquid with the very finely divided inorganicoxides, in the form of a very finely atomized aerosol.

In the process according to the invention it is possible to use veryfinely divided inorganic metal oxides, having an average primaryparticle size of up to 1 μm. Such metal oxides are preferably titaniumdioxide, aluminium oxide and silicon dioxides, such as silicas. Silicacan be prepared by wet-chemical precipitation or, pyrogenically, by theflame hydrolysis of, for example, tetrachlorosilane.

The silicas which are preferably used in the process according to theinvention have an average primary particle size of up to 250 nm,preferably less than 100 nm, and more preferably an average primaryparticle size of from 2 to 50 nm, in particular with a specific surfacearea of greater than 25 m² /g, preferably from 50 m² /g to 400 m² /g andmore preferably from 150 m² /g to 250 m² /g (measured by the BET methodin accordance with DIN 66131 and 66132). Hydrophilic or alreadysilylated silicas can be employed. Precipitation silicas orpyrogenically prepared silicas can be employed. Particular preference isgiven to pyrogenically prepared, highly disperse silicas, which areproduced pyrogenically from halosilicon compounds in a known manner asdescribed in DE 26 20 737. They are prepared by hydrolysis of silicontetrachloride in an oxyhydrogen gas flame.

The pyrogenic silica may come directly from the burner, may have beenstored or may be already in the familiar commercial packaging.

The inorganic oxide used in the process according to the invention maybe an inorganic oxide, for example pyrogenic silica, whose surface hasbeen modified with dialkylsiloxy groups, such as the modified silicaprepared in accordance with DE 42 21 716 (Wacker-Chemie GmbH) whichalready has a carbon content of less than 1% by weight per 100 m² /g ofspecific surface area (measured by the BET method in accordance with DIN66131 and 66132). Silica of this kind is more preferred. This silica maybe freshly prepared. However, this silica may also be employed as storedor as commercially packaged silica.

The silylating agent used is an organosilicon compound or a mixture oftwo or more organosilicon compounds, at least one of the organosiliconcompounds employed being relatively nonvolatile in the processtemperature range of from 0° C. to 350° C., preferably from 20° C. to250° C. and more preferably from 20° C. to 180° C. If in a preferredembodiment volatile organosilicon compounds are used, then those usedhave a boiling point below the above mentioned process temperaturerange. In this context the term process refers to the entire procedureof silylation, starting with the mixing of silica and silylating agentand comprising all of the subsequent after treatment and purificationsteps.

The organosilicon compounds employed are preferably organosilanes of theformula

    R.sup.1.sub.n SiX.sub.4-n                                  (I)

in which

R¹ is identical or different and is a monovalent, optionallyhalogenated, hydrocarbon radical having 1 to 18 carbon atoms.

X is identical or different and is a halogen, preferably chlorine, orOH, OR², OCOR², O(CH₂)_(x) OR²,

R² is identical or different and is a monovalent hydrocarbon radicalhaving 1 to 8 carbon atoms,

n is 1 or 2, preferably 2, and

x is 1, 2, or 3, preferably 1, and/or

organosiloxanes of the formula

    (R.sup.1.sub.a X.sub.b SiO.sub.1/2).sub.z (R.sup.1.sub.2 SiO.sub.2/2).sub.x (R.sup.3 R.sup.1 SiO.sub.2/2).sub.y (SiX.sub.b R.sup.1.sub.a).sub.z(II)

in which

R¹ is as defined above.

R² is as defined above,

R³ is identical or different, is a hydrogen or a monovalent, optionallyhalogenated, hydrocarbon radical having 1 to 18 carbon atoms which isdifferent from R¹,

X is as defined above, preferably OH

a is 0, 1, 2 or 3, preferably 2,

b is 0, 1, 2 or 3, preferably 1, the sum of a+b being equal to 3.

x is 0 or an integer from 1 to 200, preferably from 10 to 50,

y is 0 or an integer from 1 to 200, with x to y preferably being atleast equal to 5 to 1

and the sum x+y being equal to 0 or an integer between 1 and 200,preferably from 10 to 50,

z is 0 or 1 with the proviso that z is greater than 0 of the sum of x+yis 0, and z is preferably 1.

The preparation of the organosilanes and organosiloxanes are widelyknown and is carried out on the basis of known preparation methods.

Examples of R¹ are alkyl radicals such as the methyl radical, the ethylradical, propyl radicals such as the isopropyl or n-propyl radical,butyl radicals such as the tert-butyl or n-butyl radical, pentylradicals such as the neopentyl, isopentyl or n-pentyl radical, hexylradicals such as the n-hexyl radical, heptyl radicals such as then-heptyl radical, octyl radicals such as the 2-ethyl-hexyl or n-octylradical, decyl radicals such as the n-decyl radical, dodecyl radicalssuch as the n-dodecyl radical, hexadecyl radicals such as then-hexadecyl radical, octadecyl radicals such as the n-octadecyl radical,alkenyl radicals such as the vinyl, 2-allyl or 5-hexenyl radical, arylradicals such as the phenyl, biphenyl or naphthyl radical, alkylarylradicals such as benzyl, ethylphenyl, tolyl or xylyl radicals,halogenated alkyl radicals such as the 3-chloropropyl,3,3,3-trifluoropropyl or perfluorohexylethyl radical, or halogenatedaryl radical such as the chlorophenyl or chlorobenzyl radical. Preferredexamples of R¹ are the methyl radical, the ethyl radical, propylradicals such as the isopropyl or n-propyl radical, and butyl radicalssuch as the tert-butyl or n-butyl radical. Particular preference isgiven to the methyl radical.

Examples of R² are alkyl radicals such as the methyl radical, the ethylradical, propyl radicals such as the isopropyl or n-propyl radical,butyl radicals such as the tert-butyl or n-butyl radical, pentylradicals such as the neopentyl, isopentyl or n-pentyl radical, hexylradicals such as the n-hexyl radical, heptyl radicals such as then-heptyl radical, octyl radicals such as the 2-ethyl-hexyl or n-octylradical. Preferred examples of R² are the methyl, ethyl and propylradical. More preference is given to the methyl radical.

Examples of R³ are alkyl radicals such as the methyl radical, the ethylradical, propyl radicals such as the isopropyl or n-propyl radical,butyl radicals such as the tert-butyl or n-butyl radical, pentylradicals such as the neopentyl, isopentyl or n-pentyl radical, hexylradicals such as the n-hexyl radical, heptyl radicals such as then-heptyl radical, octyl radicals such as the 2-ethyl-hexyl or n-octylradical, decyl radicals such as the n-decyl radical, dodecyl radicalssuch as the n-dodecyl radical, hexadecyl radicals such as then-hexadecyl radical, octadecyl radicals such as the n-octadecyl radical,alkenyl radicals such as the vinyl, 2-allyl or 5-hexenyl radical, arylradicals such as the phenyl, biphenyl or naphthyl radical, alkylarylradicals such as benzyl, ethylphenyl, tolyl or xylyl radicals,halogenated alkyl radicals such as the 3-chloropropyl,3,3,3-trifluoropropyl or perfluorohexylethyl radical, or halogenatedaryl radical such as the chlorophenyl or chlorobenzyl radical. Then-octyl, n-octadecyl, the vinyl and the 3,3,3-trifluoropropyl radicalsare preferred. More preference is given to the n-octyl radical.

Examples of organosilanes in accordance with formula (I) aremethyltrichlorosilane, vinyltrichlorosilane, dimethyldichlorosilane,vinylmethyldichlorosilane, methyltrimethoxysilane,vinyltrimethoxysilane, dimethyldimethoxysilane,vinylmethyldimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane,dimethyldiethoxysilane, vinylmethylethoxysilane,methyltriacethoxysilane, dimethyldiacethoxysilane,octylmethyldichlorosilanes and octadecylmethyldichlorosilane. Preferenceis given to the dialkylsilanes, and particular preference todialkyldichlorosilanes such as dimethyldichlorosilane,octylmethyldichlorosilane and octadecylmethyldichlorosilane, and todimethyldimethoxysilane and dimethyldiethoxysilane.Dimethyldichlorosilane is more preferred.

It is also possible to employ any desired mixtures of organosilanes inany proportions. Preferred mixtures are those in which, in accordancewith formula (I), compounds where n=2 are present to the extent of morethan 80 mole %, preferably greater than 90 mole %. More preference isgiven to mixtures in which at least one compound of formula (I) in whichR¹ is different, for example a methyl group and an alkyl group having atleast 6 carbon atoms. Preferred mixtures in this case comprisedimethyldichlorosilane and octylmethyldichlorosilane in a ratio of from5:1 to 50:1.

Examples of organosiloxanes are linear or cyclic dialkylpolysiloxaneshaving an average number of dialkylsiloxy units of up to 200, preferablyfrom 5 to 100 and more preferably from 10 to 50. Preference is given tothe dialkylpolysiloxanes, among which the dimethylpolysiloxanes arepreferred. More preference is given to linear polydimethylsiloxaneshaving the following end groups: trimethylsiloxy, dimethylhydroxysiloxy,dimethylchlorosiloxy, dimethylmethoxysiloxy, dimethylethoxysiloxy,methyldichlorosiloxy, methyldimethoxysiloxy, methyldiethoxysiloxy,dimethylacetoxysiloxy and methyldiacetoxysiloxy; the end groups areidentical or different. Among the polydimethysiloxanes mentioned, morepreference is given to those having a viscosity of from 10 to 100 mPa.s,in particular from 20 to 60 mPa.s at 25° C., in which both end groupsare dimethylhydroxysiloxy groups. Any desired mixtures and proportionsof the above mentioned organosiloxanes can also be employed.

More preference is given to silylating agents or mixtures of silylatingagents, according to formulae (I) and (II), which lead, on the highlyapolar pyrogenic silica, to a covering with hydrocarbon-siloxy groups ofwhich at least 80 mole %, preferably at least 90 mole % and morepreferably at least 98 mole % are siloxy groups substituted with twohydrocarbon radicals, preferably dialkylsiloxy groups and morepreferably dimethylsiloxy groups.

In a preferred embodiment, the organosilicon compounds employed assilylating agents in the process according to formulae (I) and (II) mayrepresent a single type of an organosilane and organopolysiloxane offormula (I) or formula (II), or a mixture of at least two differenttypes of the organosilane and organosiloxane of formula (I) or formula(II), or one type of the organosilane of formula (I) and a mixture ofthe organosiloxane of formula (II) or a mixture of the organosilane offormula (I) and one type of the organosiloxane of formula (II).

All parts by weight indicated relate to 100 parts by weight of silica.

The silylating agent is preferably added in quantities of from 2 to 100parts by weight, preferably from 5 to 50 parts by weight.

In a preferred embodiment of the process according to the invention, thesilylating agents employed are relatively nonvolatile and volatileorganosilicon compounds, the term relatively nonvolatile referring tothe fact that the silylating agent does not desorb into the gas phasewithin the process temperature range; this is preferably the case at avapor pressure of from 0 mbar to 100 mbar and more preferably at a vaporpressure of from 0 mbar to 10 mbar. The silylating agent may be employedin any desired proportions of relatively nonvolatile organosiliconcompounds, and preferably comprises from 1% to 99% by weight,particularly preferably from 20% to 95% by weight and more preferablyfrom 50% to 90% by weight of nonvolatile organosilicon compounds.

In a preferred embodiment of the process according to the invention,protic solvents are employed in addition to the organosilicon compounds.These solvents may be employed in liquid, atomized or gaseous form. Theypreferably comprise water and/or lower alcohols. Mixtures of differentalcohols and mixtures of one or more alcohols with water may beemployed. The additional treatment with water, alcohol and additionalvolatile organosilicon compound may be carried out in any desiredsequence. The additional treatment with water, alcohol and additionalvolatile organosilicon compound may be carried out prior to, in the samestep as, or subsequent to the treatment with relatively nonvolatileorganosilicon compounds.

The protic solvents employed in the process according to the inventionmay preferably be lower alcohols or mixtures of different loweralcohols. Alcohols having not more than 8 carbon atoms are preferred.More preference is given to alkanols such as methanol, ethanol,isopropanol, butanol and hexanol.

The alcohols or alcohol mixtures are preferably employed in quantitiesof from 0.5 to 50 parts by weight, preferably in quantities of from 1 to20 parts by weight and more preferably in quantities of from 2 to 10parts by weight.

As protic solvent in the process according to the invention, water maybe employed as a homogeneous mixture with a lower alcohol or withmixtures of different lower alcohols. The water is preferably employedin quantities of from 0.5 to 50 parts by weight and most preferably inquantities of from 2 to 20 parts by weight. If water is employed in amixture with alcohols, the ratio of water to alcohol employed ispreferably from 1:10 to 10:1, preferably from 1:4 to 4:1. Morepreference is given to a quantity by weight of water which does notexceed the quantity by weight of silylating agent.

In the process according to the invention, the silica which is notspecially dried, may be water-moist and contains HCl gas, is set inmotion in such a way that it is fluidized by means of transportingdevices such as fans or compressed-air diaphragm pumps, or by means ofstirring, which can be carried out, for example, by paddle-stirring atfrom 10 to 5000 rpm, preferably from 100 to 2000 rpm, or fluidized in afluidized bed by a stream of gas or by a method described in DE 42 21716 (Wacker-Chemie GmbH) in a silo and mixed intensively at atemperature of from 0° C. to 350° C., preferably from 20° C. to 250° C.and more preferably from 20° C. to 180° C. with the organosiliconcompound which at this temperature is relatively nonvolatile, liquid andin the form of a very finely atomized aerosol, this organosiliconcompound being very finely distributed throughout the reaction space.The term very finely atomized organosilicon compound relates to anaverage droplet size of less than 500 μm, preferably less than 250 μmand more preferably less than 100 μm. The term aerosol refers to adisperse system in the form of an aerosol mist which comprisesliquid/gaseous phases. The liquid phase is the silylating agent and thegaseous phase is the surrounding gas, such as inert gas comprisingnitrogen and/or carbon dioxide, air, or inert gas mixtures with air.Very free atomization is brought about by means of nozzle, disc orultrasonic atomization techniques. An ultrasonic nebulizer from Lechleror discs from Niro Atomizer may be used for this purpose. Mixtures ofdifferent organosilicon compounds may be employed. This mixing operationis carried out for a residence time of from 1 second to 24 hourspreferably from 5 seconds to 60 minutes. Mixing is carried out at from100 mbar to 3 bar, preferably at atmospheric pressure.

Subsequently, following this mixing operation, the reaction is broughtto completion outside the reaction vessel in a second vessel, which mayif desired be closed, or preferably within the same reaction vessel bymeans of an after treatment, a heat treatment at a temperature of from0° C. to 400° C., preferably at from 50° C. to 350° C. and morepreferably at from 60° C. to 180° C. for a period of from 1 min to 48hours, preferably from 15 min to 6 hours. The after treatment may becarried out on the silica which is at rest, which has been set in motionby stirring or which is fluidized by means of a stream of gas,preferably a stream of inert gas, in a fluidized bed. The aftertreatment may be carried out in one or more reaction vessels.

In addition, there follows a further step of purification of the silicato remove secondary products of the reaction, which is carried out atfrom 50° C. to 400° C., preferably from 150° C. to 380° C. and morepreferably from 250° C. to 360° C. over a period of from 1 min to 6hours at a pressure of from, 0.01 mbar to atmospheric pressure,preferably at atmospheric pressure. The purification can be carried outon the silica which is at rest, which has been set in motion by stirringor which is fluidized by means of a stream of gas, preferably a streamof inert gas.

The mixing of the silica with the organosilicon compound, the aftertreatment and the purification of the silica are carried out under inertgas, preference being given to nitrogen and carbon dioxide, or inert gasmixtures with air, so that the ignition capability of the silylatingagent is removed.

The steps of the process, such as mixing, after treatment andpurification, can be carried out in the form of a batchwise orcontinuous process.

In all of the process steps, unbonded silylating agent is present incondensed, nongaseous form.

The advantages of the process according to the invention are thepreparation of a highly apolar, highly disperse silica, a completechemical fixation of the silylating agent, process temperatures below400° C., resulting in a lower energy consumption, a relatively smallproportion of volatilizable silylating agent, high reaction yields andtherefore a decreased pollution of the waste gas with silylating agent,which is more economic and less harmful to the environment.

A homogeneous reaction of the relatively nonvolatile organosiliconcompound takes place on the surface of the silica. Despite the additionof the relatively nonvolatile organosilicon compound for the surfacetreatment of the silica, a better, higher reaction yield, a higherdegree of apolarity and a better rheological effect of the silica isobtained than by using the correspondingly (measured on the basis ofcarbon content) equal quantity of organosilicon compound which is addedonly in gas form but is otherwise chemically identical. In addition,despite the use of a relatively nonvolatile organosilicon compound, nofractions of organosilicon compound which are not chemically bonded, andtherefore soluble, can be found on the finished silica.

The highly apolar, finely divided inorganic oxide which is prepared bythis process is preferably highly apolar silica, more preferably highlyapolar, pyrogenic silica having an average primary particle size of lessthan 100 nm, preferably having an average primary particle size of from2 to 50 nm and more preferably having an average primary particle sizeof from 5 to 20 nm, in particular with a specific surface area ofgreater than 25 m² /g, preferably from 50 to 300 m² /g and morepreferably from 100 to 200 m² /g (measured by the BET method inaccordance with DIN 66131 and 66132). The highly apolar silica accordingto the invention has, per 100 m² /g specific surface area (measured bythe BET method in accordance with DIN 66131 and 66132), a carbon contentof at least 1% by weight, preferably at least 1.5% by weight and morepreferably at least 2.0% by weight. No isolated silanol groups can bedetected at a wave number of 3750 cm⁻¹ on the silica by means of IRspectroscopy. Even after prolonged intense contact with water, forexample shaking, the silica has no water-wettable fractions. The silicaexhibits a methanol number (Appendix III) of greater than or equal to50, preferably greater than 65 and more preferably greater than 75. Thesilylating agent on the silica is firmly fixed chemically and completelyand has no component which can be extracted from the silica or issoluble (Appendix I). The highly apolar silica according to theinvention displays a low residual content of relative sorption capacityfor hydroxyl ions (Appendix II). This residual content is less than 25%,preferably less than 15%, of the initial value of sorption capacity forhydroxyl ions as found for untreated hydrophilic silica. In accordancewith these characteristics, the silica according to the invention can bedesignated as completely apolar or highly apolar. The silica accordingto the invention is characterized in that it has a high thickeningeffect, especially in polar systems such as aqueous solutions, forexample in mixtures of water with lower alcohols such as methanol,ethanol, isopropanol and n-propanol, especially those having a watercontent of more than 50% by weight, in aqueous dispersions andemulsions, but also in other polar systems such as polyesters, vinylesters, epoxides and polyurethanes. In a more preferred embodiment thehighly apolar silica silylated with dialkylsiloxy units is characterizedin that it has a higher thickening effect than those silicas which aremodified with trialkylsiloxy units and which have the same sorptioncapacity for hydroxyl ions.

Preference is given to a highly apolar pyrogenic silica in which atleast 80 mole % of the bonded silylating agent comprises siloxy groupssubstituted with two hydrocarbon radicals.

The hydrocarbon radicals are preferably the radicals R¹ and R³ asdefined above.

The highly apolar silica according to the invention, when used as arheological additive, shows no defects of adhesion or intercoatadhesion, and also no defects in overcoatability (e.g., cratering),which may occur because of the migration of nonbonded silylating agentconstituents.

Silicas are preferably employed as a theological additive in apolarsystems. In apolar systems the establishment of the viscosity by silicatakes place in particular by means of hydrogen bonds between the surfacesilanol groups of the silica particles. In polar systems the surfacesilanol groups of the silica may lead to a collapse in the viscosity. Itis therefore known that hydrophilic silicas do not give a satisfactoryaction as rheological additive in polar systems such as aqueousalcohols, or in epoxy resins, vinyl ester resins or polyurethanes.Especially after a prolonged storage period, there is a reduction in theviscosity accompanied by a sharp decrease in the flow limit. This leadsto low stability at relatively high coat thicknesses on verticalsurfaces and consequently to unwanted running on curing. Conventionalsilylated silicas likewise achieve no satisfactory rheologicaleffectiveness here after prolonged storage.

The invention also relates to the use of highly apolar, pyrogenic silicaprepared by the process according to the invention as thickener in polarsystems, as an absorbent for oils, for improving the flowability oftoners and in antifoam compositions.

The highly apolar, pyrogenic silica prepared by the process according tothe invention exhibits a pronounced increase in viscosity, especiallyfor polar liquid or pasty media which are composed of those chemicalcompounds which are able to form hydrogen bonds or undergo dipolarinteractions, examples being epoxy resins, polyurethanes or polyvinylester resins, and leads to the development of a flow limit and tothixotropy in such systems.

The highly apolar silica according to the invention is thereforeemployed as a rheological additive, for example, in polar polymer, resinand solvent systems such as epoxy resins, polyurethanes, vinyl esterresins and other comparable systems in order to achieve a level ofviscosity which is high and is stable over time on storage, structuralviscosity and a flow limit.

The invention relates in general to all solvent-free,solvent-containing, water-dilutable, film-forming coating compositions,rubbery to hard coatings, adhesives, sealing and casting compositionsand to other comparable systems. It relates to systems of low to highpolarity which contain silica as viscosity-imparting component.

The invention relates in particular to systems such as:

Epoxy systems

The epoxy systems are solvent-containing or solvent-free,water-dilutable reactive systems, such as epoxide/phenol, epoxide/amine,epoxide isocyanate baking systems, epoxide/ester and amine curing agentsfor epoxy resins, such as aliphatic, cycloaliphatic orheterocycloaliphatic polyamines.

Polyurethane systems (PUR)

The polyurethane systems are PUR 1-component systems based onoil-modified urethanes, which cure by oxidation, as cold curing, by wayof an unsaturated oil component, PUR 1-component systems which aremoisture-curing, and cold curing occurs by atmospheric moisture by wayof isocyanate groups, PUR 1-component systems based on blockedpolyisocyanates, which cure, as cold curing, by deblocking of theisocyanate groups with aliphatic hydroxyl groups, PUR 1-componentsystems which dry physically by evaporation at room temperature, PUR1-component systems on an aqueous basis (PUR ionomers), which curephysically by the water being removed on drying, or PUR 2-componentsystems comprising isocyanate prepolymers and polyhydroxy compounds.

Vinyl ester resins

In contrast to the conventional, unsaturated polyester resins, the useof hydrophilic or conventional silylated silica as a rheologicaladditive in vinyl ester resins presents numerous difficulties.

The highly apolar silica according to the invention, as rheologicaladditive in these systems, provides the desired and required viscosity,structural viscosity, thixotropy and an adequate flow limit forstability on vertical surfaces. This continues to be the case even whenthe systems are stored for a prolonged period. The silica according tothe invention is superior to silica which is hydrophilic and notsilylated in accordance with the invention.

In this context, the silica according to the invention provides theseproperties as a theological additive without leading to defects inadhesion or intercoat adhesion. Defects in overcoatability (e.g.cratering), which may occur because of the migration of nonbondedconstituents of the silylating agent, are not observed with the silicaaccording to the invention.

In addition, the silica according to the invention can be used as anabsorbent for mineral oils, silicone oils and bio oils. The silicaaccording to the invention is suitable for improving the flowability oftoners. Furthermore, it is suitable as silica in antifoam compositions,preferably for aqueous systems such as detergents.

EXAMPLE 1

4.5 g of water in liquid, very finely atomized form, 16.0 g of methanolin liquid, very finely atomized form and 32.0 g ofdimethyldichlorosilane (commercially available under the name WACKERSilan M2 from Wacker-Chemic GmbH, Munich, D) in liquid, very finelyatomized form are mixed at a temperature of 30° C. over 15 minutes into100 g of a pyrogenic silica which is fluidized by stirring at 1000 rpm(paddle stirrer, 6 liter vessel) and has a specific surface area of 200m² /g (measured by the BET method in accordance with DIN 66131 and66132), a thickening effect in UP resin⁸) of 6000 mPa.s and a thickeningeffect in 25% ethanol⁹) of 10 mPa.s, and which can be prepared inaccordance with DE 26 20 737 (commercially available under the nameWACKER HDK N20 from Wacker-Chemie GmbH, Munich, D). The very fineatomization is brought about by means of a solid-cone nozzle with a 0.1mm bore and by a pressure of 10 bar. The silica loaded in this way isfirst heat-treated at 60° C. for 180 min in a drying oven, and thenpurified in a fluidized bed in a stream of nitrogen of 2.5 cm/s at 60°C. for 180 min. The quantity of silylating agent employed corresponds,at 100% by weight reaction yield, to a carbon content in the silica of %by weight C_(theoretical) =5% by weight (% by weight C_(theoretical)/100=quantity of dimethyldichlorosilane (g) * 0.186 divided by100+quantity of dimethyldichlorosilane (g) * 0.574). The elementalanalysis of the silica for carbon is measured by incinerating the silicain oxygen at 1000° C., and the carbon dioxide formed is determined byinfrared spectroscopy (Leco CS 244 instrument). The elemental analysisshows, based on the silica-bonded silylating agent, a reaction yield of60%.

Analytical data of the silica

    ______________________________________                                        Appearance           loose white powder                                       Surface area by BET.sup.1)                                                                         160 m.sup.2 /g                                           Tamping density.sup.2)                                                                             55 g/l                                                   Loss on drying.sup.3) (2 h at 230° C.)                                                      <0.1% by weight                                          Carbon content       3.0% by weight                                           pH.sup.4) (in 4% dispersion)                                                                       4.5                                                      IR band (DRIFT) at 3750 cm.sup.-1                                                                  not detectable                                           Extractable silylating agent.sup.5)                                                                not detectable                                           Rel. sorption capacity.sup.6) for OH.sup.-                                                         22%                                                      Methanol number.sup.7)                                                                             55                                                       Thickening effect in UP resin.sup.8)                                                               5500 mPa.s                                               Thickening effect in 25% ethanol.sup.9)                                                            800 mPa.s                                                ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 2

(not according to the invention)

4.5 g of water and 16.0 g of methanol in liquid, finely atomized formand 32.00 g of dimethyldichlorosilane (commercially available under thename WACKER Silan M2 from Wacker-Chemie GmbH, Munich, D) in gaseous formare mixed at a temperature of 100° C. over 15 minutes into 100 g of apyrogenic silica which is fluidized by stirring at 1000 rpm (paddlestirrer, 6 liter vessel) and has a specific surface area of 200 m² /g(measured by the BET method in accordance with DIN 66131 and 66132), athickening effect in UP resins⁸) of 6000 mPa.s and a thickening effectin 25% ethanol⁹) of 10 mPa.2, and which can be prepared according to DE26 20 737 (commercially available under the name WACKER HDK N20 fromWacker-Chemie GmbH, Munich, D). The silica loaded in this way is firstof all heat-treated at 100° C. in a drying oven for 180 min, and then ispurified in a fluidized bed in a stream of nitrogen of 2.5 cm/s at 100°C. for 180 min. The quantity of silylating agent employed corresponds,at a theoretical reaction yield of 100% by weight, to a carbon contentin the silica of % by weight C_(theoretical) =5% by weight (% by weightC_(theoretical) /100=quantity of dimethyldichlorosilane (g) * 0.186divided by 100+quantity of dimethyldichlorosilane (g) * 0.574). Theelemental analysis of the silica for carbon shows a reaction yield,based on the silica-bonded silylating agent, of 30%.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          180 m.sup.2 /g                                          Tamping density.sup.2)                                                                              50 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       0.5% by weight                                          Carbon content        1.5% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.2                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   present                                                 Extractable silylating agent residues.sup.5)                                                        detectable                                              Rel. sorption capacity.sup.6) for OH.sup.-                                                          45%                                                     Methanol number.sup.7)                                                                              40                                                      Thickening effect in UP resin.sup.8)                                                                3500 mPa.s                                              Thickening effect in 25% ethanol.sup.9)                                                             300 mPa.s                                               ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 3

15.5 g of a dimethylorganosiloxane which contains no reactive end groupsand is in relatively nonvolatile, very finely atomized form are mixed ata temperature of 180° C. over 15 minutes into 100 g of a pyrogenicsilica which is fluidized by stirring at 1000 rpm (paddle stirrer, 6liter vessel) and has a specific surface area of 200 m² /g (measured bythe BET method in accordance with DIN 66131 and 66132), a thickeningeffect in UP resins⁸) of 6000 mPa.s and a thickening effect in 25%ethanol⁹) of 10 mPa.s, and which can be prepared according to DE 26 20737 (commercially available under the name WACKER HDK N20 fromWacker-Chemie OmbH, Munich, D). The dimethylorganosiloxane employed is apolydimethylsiloxane end-blocked with trimethylsiloxy groups and havinga viscosity at 25° C. of 10 mPa.s (commercially available under the nameWACKER Siliconol silicone oil! AK 10 from Wacker-Chemie GmbH, Munich,D). The very free atomization is brought about in this case by means ofa solid-cone nozzle with a 0.1 mm bore and by a pressure of 15 bar. TheAK 10 silicone oil employed shows a volatility at this temperature ofless than 0.5% by weight. The silica loaded in this way is stirred at180° C. for a further 15 minutes and then is purified with gentlenitrogen flushing at 300° C. for 120 min in a drying oven. The quantityof silylating agent employed corresponds, at a reaction yield of 100% byweight, to a carbon content in the silica of % by weight C_(theoretical)=5% by weight (% by weight C_(theoretical) /100=quantity ofdimethylorganosiloxane (g) * 0.324 divided by 100+quantity ofdimethylorganosiloxane (g). The elemental analysis of the silica forcarbon shows a reaction yield, based on the silica-bonded silylatingagent, of 64%.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          170 m.sup.2 /g                                          Tamping density.sup.2)                                                                              55 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       <0.1% by weight                                         Carbon content        3.2% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.3                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   not detectable                                          Extractable silylating agent residues.sup.5)                                                        not detectable                                          Rel. sorption capacity.sup.6) for OH.sup.-                                                          24%                                                     Methanol number.sup.7)                                                                              55                                                      Thickening effect in UP resin.sup.8)                                                                4600 mPa.s                                              Thickening effect in 25% ethanol.sup.9)                                                             800 mPa.s                                               ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 4

(not according to the invention)

15.5 g of a dimethylorganosiloxane which contains no reactive end groupsand is in volatile form are mixed at a temperature of 180° C. over 15minutes into 100 g of a pyrogenic silica which is fluidized by stirringat 1000 rpm (paddle stirrer, 6 liter vessel) and has a specific surfacearea of 200 m² /g (measured by the BET method in accordance with DIN66131 and 66132), a thickening effect in UP resin⁸) of 6500 mPa.s and athickening effect in 25% ethanol ⁹) of 10 mPa.s, and which can beprepared according to DE 26 20 737 (commercially available under thename WACKER HDK N20 from Wacker-Chemie GmbH, Munich, D). Thedimethylorganosiloxane employed is octamethylcyclotetrasiloxane. Thesilica loaded in this way is stirred at 180° C. for an additional 15minutes and then purified with gentle nitrogen flushing at 300° C. for120 min in a drying oven. The quantity of silylating agent employedcorresponds, at a reaction yield of 100% by weight, to a carbon contentin the silica of % by weight C_(theoretical) =5% by weight (% by weightC_(theoretical) /100=quantity of dimethylorganosiloxane (g) * 0.324divided by 100+quantity of dimethylorganosiloxane (g)). The elementalanalysis of the silica for carbon shows a reaction yield, based on thesilica-bonded silylating agent, of 34% by weight.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          185 m.sup.2 /g                                          Tamping density.sup.2)                                                                              48 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       <0.1% by weight                                         Carbon content        1.7% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.3                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   present                                                 Extractable silylating agent residues.sup.5)                                                        detectable                                              Rel. sorption capacity.sup.6) for OH.sup.-                                                          62%                                                     Methanol number.sup.7)                                                                              35                                                      Thickening effect in UP resin.sup.8)                                                                3500 mPa.s                                              Thickening effect in 25% ethanol.sup.9)                                                             200 mPa.s                                               ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 5

75 g/h of OH-terminal polydimethylsiloxane having a viscosity of 40mPa.s at 25° C. (commercially available under the name WACKERWeichmacher plasticizer! X 345 from Wacker-Chemie GmbH, D) in a mixtureof 1 to 1000 parts by volume with nitrogen at a pressure of 10 bar isadded at a temperature of 100° C. in liquid, very finely atomized formwith a solid-cone nozzle with 0.1 mm bore to a mass flow of 1000 g/h ofa pyrogenic silica which is fluidized by nitrogen at an empty-pipe gasrate of 0.1 cm/s and having a specific surface area of 200 m² /g(measured by the BET method in accordance with DIN 66131 and 66132), athickening effect in UP resin ⁸) of 6500 mPa.s and a thickening effectin 25% ethanol⁹) of 10 mPa.s, and which can be prepared according to DE26 20 737 (commercially available under the same WACKER HDK N20 fromWacker-Chemie GmbH, Munich, D), and 60 g/h of steam, 30 g/h of methanolvapor and 135 g/h of dimethyldichlorosilane (commercially availableunder the name WACKER Silan M2 from Wacker-Chemie GmbH, Munich, D) aremixed in in gaseous form. The residence time of the silica loaded inthis way at 100° C. is 2 hours. The silica is subsequently purified inan adjacent, further reaction vessel at 300° C. for 30 minutes,fluidized by nitrogen at an empty-pipe gas rate of 1.0 cm/s, and in athird reaction vessel at 300° C. for 15 min, by fluidization with anair/nitrogen mixture at an empty-pipe gas rate of 2.5 cm/s. The quantityof silylating agent employed corresponds, at a reaction yield of 100% byweight, to a carbon content in the silica of % by weight C_(theoretical)=5% by weight (% by weight C_(theoretical) /100=quantity ofdimethyldichlorosilane (g) * 0.186+quantity of polydimethylsiloxane(g) * 0.324 divided by 100+quantity of polydimethylsiloxane (g)+quantityof dimethyldichlorosilane (g) * 0.574). The elemental analysis of thesilica for carbon shows a reaction yield, based on the silica-bondedsilylating agent, of 88% by weight.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          125 m.sup.2 /g                                          Tamping density.sup.2)                                                                              55 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       <0.1% by weight                                         Carbon content        4.4% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.4                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   not detectable                                          Extractable silylating agent residues.sup.5)                                                        not detectable                                          Rel. sorption capacity.sup.6) for OH.sup.-                                                          13%                                                     Methanol number.sup.7)                                                                              80                                                      Thickening effect in UP resin.sup.8)                                                                7800 mPa.s                                              Thickening effect in 25% ethanol.sup.9)                                                             1800 mPa.s                                              ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 6

g of OH-terminal reactive polydimethylsiloxane having a viscosity of 40mPa.s at 25° C. (commercially available under the name WACKERWeichmacher plasticizer!X 345 from Wacker-Chemie GmbH, D) in the form ofliquid droplets which are very finely atomized using a disc atomizer andwhich have an average radius of less than 100 μm, 10.0 g of water inliquid, very finely atomized form, 10.0 g of methanol in liquid, veryfinely atomized form, and 10.0 g of dimethyldichlorosilane (commerciallyavailable under the name WACKER Silan M2 from Wacker-Chemie GmbH,Munich, D) in liquid, very finely atomized form are mixed at atemperature of 30° C. over 20 minutes by means of a solid-cone nozzlewith a 0.1 mm bore and by a pressure of 10 bar into 100 g of a pyrogenicsilica which is fluidized by stirring at 1000 rpm (paddle stirrer, 6liter vessel) and has a specific surface area of 200 m² /g (measured bythe BET method in accordance with DIN 66131 and 66132), a thickeningeffect in UP resins⁸) of 6500 mPa.s and a thickening effect in 25%ethanol⁹) of 10 mPa.s, and which can be prepared according to DE 26 20737 (commercially available under the name WACKER HDK N20 fromWacker-Chemic GMbH, Munich, D). The silica loaded in this way isheat-treated at 100° C. for 120 min in a drying oven, and then purifiedwith gentle nitrogen flushing at 300° C. for 120 min in a drying oven.The quantity of silylating agent employed corresponds, at a reactionyield of 100% by weight to a carbon content of the silica of % by weightC_(theoretical) =5.1% by weight (% by weight C_(theoretical)/100=quantity of dimethyldichlorosilane (g) * 0.186+quantity ofpolydimethylsiloxane (g) * 0.324 divided by 100+quantity ofpolydimethylsiloxane (g)+quantity of dimethyldichlorosilane (g) * 0.574.The elemental analysis of the silica for carbon shows a reaction yield,based on the silica-bonded silylating agent, of 95% by weight.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          118 m.sup.2 /g                                          Tamping density.sup.2)                                                                              52 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       <0.1% by weight                                         Carbon content        4.8% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.6                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   not detectable                                          Extractable silylating agent residues.sup.5)                                                        not detectable                                          Rel. sorption capacity.sup.6) for OH.sup.-                                                          11%                                                     Methanol number.sup.7)                                                                              80                                                      Thickening effect in UP resin.sup.8)                                                                7600 mPa.s                                              Thickening effect in 25% ethanol.sup.9)                                                             1900 mPa.s                                              ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 7

(not according to the invention)

10 g of OH-terminal polydimethylsiloxane having viscosity of 40 mPa.s at25° C. (commercially available under the name WACKER Weichmacherplasticizer! X 345 from Wacker-Chemie GmbH, D) in the form of liquiddroplets having an average droplet diameter of greater than 500 μm aresprayed at a temperature of 30° C. over 20 minutes via a nozzle into 100g of a pyrogenic silica which is fluidized by stirring at 1000 rpm(paddle stirrer, 6 liter vessel) and has a specific surface area of 200m² /g (measured by the BET method according to DIN 66131 and 66132), athickening effect in UP resin⁸) of 6500 mPa.s and a thickening effect in25% ethanol⁹) of 10 mPa.s, and which can be prepared according to DE 2620 737 (commercially available under the name WACKER HDK N20 fromWacker-Chemie GmbH, Munich, D), and 10.0 g of water in liquid, veryfinely atomized form, 10.0 g of methanol in liquid, very finely atomizedform and 10.0 g of methanol in liquid, very finely atomized form and10.0 g of dimethyldichlorosilane (commercially available under the nameWACKER Silan M2 from Wacker-Chemie GmbH, Munich, D) in liquid, veryfinely atomized form are mixed by means of a solid-cone nozzle with a0.1 mm bore and by a pressure of 10 bar. The silica loaded in this wayis heat-treated at 100° C. for 120 min in a drying oven, and then ispurified with gentle nitrogen flushing at 300° C. for 120 min in adrying oven. The quantity of silylating agent employed corresponds, at areaction yield of 100% by weight, to a carbon content in the silica of %by weight C_(theoretical) =5.1% by weight (% by weight C_(theoretical)/100=quantity of dimethyldichlorosilane (g) * 0.186+quantity ofpolydimethylsiloxane (g) * 0.324 divided by 100+quantity ofpolydimethylsiloxane (g)+quantity of dimethyldichlorosilane (g) *0.574). The elemental analysis of the silica for carbon shows a reactionyield, based on the silica-bonded silylating agent, of 35% by weight.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          183 m.sup.2 /g                                          Tamping density.sup.2)                                                                              65 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       <1.6% by weight                                         Carbon content        1.7% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.6                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   not detectable                                          Extractable silylating agent residues.sup.5)                                                        not detectable                                          Rel. sorption capacity.sup.6) for OH.sup.-                                                          52%                                                     Methanol number.sup.7)                                                                              40                                                      Thickening effect in UP resin.sup.8)                                                                3600 mPa.s                                              Thickening effect in 25% ethanol.sup.9)                                                             400 mPa.s                                               ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 8

10 g of OH-terminal polydimethylsiloxane having a viscosity of 40 mPa.sat 25° C. (commercially available under the name WACKER Weichmacherplasticizer! X 345 from Wacker-Chemie GmbH, D) in the form of liquiddroplets, very finely atomized with a disc atomizer and having anaverage radius of less than 100 μm, and 10.0 g of water in liquid, veryfinely atomized form, 10.0 g of methanol in liquid, very finely atomizedform and 10.0 g of dimethyldichloro-silane (commercially available underthe name WACKER Silan M2 from Wacker-Chemie GmbH, Munich, D) in liquid,very finely atomized form are mixed at a temperature of 30° C. over 20minutes by means of a solid-cone nozzle with a 0.1 mm bore and by apressure of 10 bar into 100 g of a pyro-genic silica which is fluidizedby stirring at 1000 rpm (paddle stirrer, 6 liter vessel), issurface-modified with dimethylsiloxy groups and has a carbon content of1.0% by weight, a specific surface area of 160 m² /g (measured by theBET method in accordance with DIN 66131 and 66132), a thickening effectin UP resins⁸) of 4000 mPa.s and a thickening effect in 25% ethanol⁹) of200 mPa.s, which can be prepared according to DE 42 21 716 (commerciallyavailable under the name WACKER HDK H20 from Wacker-Chemie GmbH, Munich,D). The silica loaded in this way is heat-treated at 100° C. for 120 minin a drying oven, and then purified with gentle nitrogen flushing at300° C. for 120 min in a drying oven. The quantity of silylating agentemployed corresponds, at a reaction yield of 100% by weight, to a carboncontent in the silica of % by weight C_(theoretical) -1.0% byweight=5.1% by weight (% by weight C_(theoretical) /100=quantity ofdimethyldichlorosilane (g) * 0.186+quantity of polydimethylsiloxane(g) * 0.324 divided by 100+quantity of dimethyldichlorosilane (g) *0.574+quantity of polydimethylsiloxane (g). The elemental analysis ofthe silica for carbon shows a reaction yield, based on the silylatingagent which is additionally silica-bonded in the treatment, of 92% byweight.

Analytical data of the silica

    ______________________________________                                        Appearance            loose white powder                                      Surface area by BET.sup.1)                                                                          105 m.sup.2 /g                                          Tamping density.sup.2)                                                                              42 g/l                                                  Loss on drying.sup.3) (2 h at 230° C.)                                                       <1.0% by weight                                         Carbon content        5.7% by weight                                          pH.sup.4) (in 4% dispersion)                                                                        4.8                                                     IR band (DRIFT) at 3750 cm.sup.-1                                                                   not detectable                                          Extractable silylating agent residues.sup.5)                                                        not detectabie                                          Rel. sorption capacity.sup.6) for OH.sup.-                                                          8%                                                      Methanol number.sup.7)                                                                              85                                                      Thickening effect in UP resin.sup.8)                                                                10,600 mPa.s                                            Thickening effect in 25% ethanol.sup.9)                                                             2900 mPa.s                                              ______________________________________                                         .sup.1) in accordance with DIN 66131 and 66132                                .sup.2) in accordance with DIN ISO 787/XI, JIS K 5101/18                      .sup.3) in accordance with DIN ISO 787/II, ASTM D 280, JIS K 5101/21          .sup.4) in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24         .sup.5) see Appendix I                                                        .sup.6) see Appendix II                                                       .sup.7) see Appendix III                                                      .sup.8) see Appendix IV                                                       .sup.9) see Appendix V                                                   

EXAMPLE 9 to 16

In order to investigate the silica in a solvent-free epoxy-polyaminoamide system, 210 g of an epoxy resin (based on bisphenol A andepichlorohydrin) having a viscosity at 25° C. of 9000 mPa.s and anepoxide value in accordance with DIN 53188 of 0.54 (commerciallyavailable under the name Europox 730 Schering AG, Bergkamen, D) , 2.10 gof a blue phthalocyanine color pigment (commercially available under thename Heliogenblau L 6700T BASF, Stuttgart, D) and 8.4 g of silicaprepared according to Examples 1 to 8, are introduced cooling and withthe dissolver (commercially available under the name Dispermat F105,Getzmann, Reichshof-Heienbach, D) running, at room temperature over 5min. (toothed disc with a diameter of 5 cm, speed of rotation 2800 rpm)and subsequently dispersed on a triple roll mill (Exakt 80 S,Exakt-Apperatebau Otto Herrmann, Norderstedt, D) (roll nip at the front:2 mm, at the back: 3 mm, speed of rotation 80 rpm, 3 passes). For thedetermination of the "viscosity before storage" and for thedetermination of the "layer thickness on vertical surfaces beforestorage" or, for the determination of the "layer thickness on verticalsurfaces after storage", after storage for 14 days at 60° C. 50 g of apolyamino amide having a viscosity at 25° C. of 550 mPa.s and an aminenumber in accordance with DIN 16945 of 440 (commercially available underthe name Eurodur 250 (Schering AG, Bergkamen, D) are mixed in at 25° C.over 5 minutes using a mixer having a blade stirrer with a diameter of70 mm (commercially available under the name IKA RW27 from Janke undKunkel, D) at 400 rpm. Immediately thereafter, the composition preparedin this way is divided, and one part is used to determine the viscositywhile the other part is used to determine the layer thickness onvertical surfaces.

Determination of the viscosity: The viscosity of the composition ismeasured using a Brookfield viscometer RVT DV-II, spindle 6, at 25° C.

Determination of the layer thickness on vertical surfaces: Using steppeddoctor blades, the composition is coated onto a black/white contrastcard in layer thicknesses of from 600 to 2600 μm (subdivided into stepsof 100 μm each time) and the card is placed in a vertical position.

The parameter recorded is the layer thickness, in micrometers (μm), atwhich the applied composition begins to flow before it is fully cured.

The viscosities and layer thicknesses on vertical surfaces, measuredbefore and after storage, are compiled in Table 1.

EXAMPLES 17

The procedure of Example 9 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with dimethylsiloxy groups and has a carbon contentof 1.0% by weight and a specific surface area of 160 m² /g (measured bythe BET method in accordance with DIN 66131 and 66132), and which can beprepared according to DE 42 21 716 (commercially available under thename WACKER HDK H20 from Wacker-Chemie GmbH, Munich, D). The results aregiven in Table 1.

EXAMPLE 18

The procedure of Example 9 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with trimethylsiloxy groups and has a carbon contentof 2.5% by weight and a specific surface area of 140 m² /g (measured bythe BET method in accordance with DIN 66131 and 66132), and which can beprepared according to DE 23 44 388 (commercially available under thename WACKER HDK H2000 from Wacker-Chemie GmbH, Munich, D). The resultsare given in Table 1.

EXAMPLE 19

The procedure of Example 9 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with ammonium-functional organopolysiloxane and hasa carbon content of 5.5% by weight and a specific surface area of 110 m²/g (measured by the BET method in accordance with DIN 66131 and 66132),and which can be prepared according to DE-A 37 07 226 (commerciallyavailable under the name WACKER HDK H2050 EP from Wacker-Chemie GmbH,Munich, D). The results are given in Table 1.

EXAMPLE 20

The procedure of Example 9 is repeated but employing, instead of asilica prepared in accordance with Example 1, a hydrophilic pyrogenicsilica having a specific surface area of 200 m² /g (measured by the BETmethod in accordance with DIN 66131 and 66132), and which can beprepared according to DE 26 20 737 (commercially available under thename WACKER HDK N20 from Wacker-Chemie GmbH, Munich, D). The results aregiven in Table 1.

The following Table indicates the viscosity (mPa.s) and layer thickness(μm) on vertical surfaces before and after storage for 14 days at 60° C.

                  TABLE I                                                         ______________________________________                                        (Viscosity (mPa.s)  Layer Thickness (μm)                                   Examples                                                                             before storage                                                                           after storage                                                                           before storage                                                                         after storage                            ______________________________________                                        9      17,000     14,600    1,700    1,200                                    10     10,300     6,900     900      <600                                     11     16,300     13,800    1,600    1,200                                    12     9,700      6,800     1,000    <600                                     13     21,200     21,100    2,200    2,100                                    14     19,900     19,300    2,100    2,100                                    15     10,200     6,200     800      <600                                     16     23,800     23,200    2,500    2,400                                    17     9,900      7,900     800      <600                                     18     5,800      5,200     <600     <600                                     19     5,100      5,100     <600     <600                                     20     18,700     5,600     2,100    <600                                     ______________________________________                                    

EXAMPLES 21 to 28

In order to investigate the silica in a 2-component polyurethane coatingcomposition, 202.67 g of a solvent-free, branches polyalcohol containingether and ester groups and having an OH content of 5% by weight, anequivalent weight of 340, an acid number of 2 and a viscosity at 20° C.of 4900 mPa.s at a shear gradient of 147 s⁻¹ (commercially availableunder the name Desmophen 1150 from Bayer AG, Leverkusen, D), 40.00 g ofmolecular sieve paste having a viscosity at 20° C. of 18,000 mPa.s andconsisting of 50% by weight of a zeolite having an average pore diameterof 0.3 nm, in castor oil (commercially available under the nameBaylith-L-Paste from Bayer AG, Leverkusen, D), 8.10 g of silica preparedin accordance with Examples 1 to 8, 176.00 g of barium sulphate fillerhaving an average particle size of 8 μm (commercially available underthe name Schwerspat heavy spar! C7 from Sachtleben Chemie GmbH,Duisburg, D), 24.00 g of futile pigment with a titanium dioxide contentof 92% by weight (commercially available under the name Kronos RN 57from Kronos Titan-GmbH, Leverkusen, D) and 2.27 g of a mixed pigment ofiron(III) oxide and manganese(III) oxide having an iron(III) oxidecontent of 59% by weight and an average particle size of 6 μm(commercially available under the name Bayferrox 303T from Bayer AG,Leverkusen, D) are introduced in succession with the dissolver(commercially available under the name Dispermat F105, Getzmann,Reichshof-Heienbach, D) running and the mixture is predispersed at roomtemperature for 10 min (toothed-disc dissolver having a diameter of 5cm, speed of rotation 2800 rpm) and then subjected to a main dispersionon the triple roll (Exakt 80 S, Exakt-Apperatebau Otto Herrmann,Norderstedt, D) (roll nip at the front: 2 mm, at the back: 3 mm, speedof rotation 80 rpm, 3 passes).

To determine the "viscosity before storage", the "layer thickness onvertical surfaces before storage" or, the "viscosity after storage" andthe "layer thickness on vertical surfaces after storage" after storageat 60° C. for 14 days, 39.60 g of a solvent-free polyisocyanate based ondiphenylmethane diisocyanate and having a content of isocyanate groupsof 31.5% by weight and a viscosity at 23° C. of 120 mPa.s (commerciallyavailable under the name Desmodur VL from Bayer AG, Leverkusen, D) aremixed in at 25° C. over 5 minutes with a mixer having a blade stirrer of70 mm in diameter (commercially available under the name IKA RW 27 fromJanke und Kunkel, D) at 400 rpm. The composition is divided and one partis used to determine the viscosity while the other part is used todetermine the layer thickness on vertical surfaces.

Determination of the viscosity: The viscosity of the composition ismeasured using a Brookfield viscometer RVT DV-II, spindle 6, at 25° C.

Determination of the layer thickness on vertical surfaces: Using steppeddoctor blades, the composition is coated onto a black/white contrastcard in layer thicknesses of from 600 μm to 2600 μm (subdivided intosteps of 100 μm) and the card is placed in a vertical position. Theparameter recorded is the layer thickness, in micrometers (μm), at whichthe applied mass begins to flow before it is fully cured.

The viscosities and the layer thickness on vertical surfaces which aremeasured before and after storage are compiled in Table 2.

EXAMPLE 29

The procedure of Example 21 is repeated but employing, instead of asilica prepared as in Example 1, a pyrogenic silica which issurface-modified with dimethylsiloxy groups and has a carbon content of1.0% by weight and a specific surface area of 160 m² /g (measured by theBET method in accordance with DIN 66131 and 66132), and which can beprepared according to DE 42 21 716 (commercially available under thename WACKER HDK H20 from Wacker-Chemie GmbH, Munich, D). The results aregiven in Table. 2.

EXAMPLE 30

The procedure of Example 21 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with trimethylsiloxy groups and has a carbon contentof 2.5% by weight and a specific surface area of 140 m² /g (measured bythe BET method in accordance with DIN 66131 and 66132), and which can beprepared according to DE 23 44 388 (commercially available under thename WACKER HDK H2000 from Wacker-Chemie GmbH, Munich, D). The resultsare given in Table 2.

EXAMPLE 31

The procedure of Example 21 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with ammonium-functional organopolysiloxane and hasa carbon content of 5.5% by weight and a specific surface area of 110 m²/g (measured by the BET method in accordance with DIN 66131 and 66132),and which can be prepared according to DE-A 37 07 226 (commerciallyavailable under the name WACKER HDK H2050 EP from Wacker-Chemie GmbH,Munich, D). The measured results are given in Table 2.

EXAMPLE 32

The procedure of Example 21 is repeated but employing, instead of asilica prepared in accordance with Example 1, a hydrophilic pyrogenicsilica having a specific surface area of 200 m² /g (measured by the BETmethod in accordance with DIN 66131 and 66132), and which can beprepared according to DE 26 20 737 (commercially available under thename WACKER HDK N20 from Wacker-Chemie GmbH, Munich, D). The results aregiven in Table 2. Table 2 shows the viscosity (mPa.s) and layerthickness (μm) on vertical surfaces before and after storage for 14 daysat 60° C.

                  TABLE 2                                                         ______________________________________                                        (Viscosity (mPa.s)  Layer Thickness (μm)                                   Examples                                                                             before storage                                                                           after storage                                                                           before storage                                                                         after storage                            ______________________________________                                        21     28,200     25,100    1,800    1,700                                    22     10,800     7,900     <600     <600                                     23     27,900     24,900    1,900    1,600                                    24     9,800      6,400     <600     <600                                     25     41,900     40,800    2,500    2,400                                    26     41,400     41,000    2,500    2,400                                    21     10,900     6,900     <600     <600                                     28     43,000     42,300    2,500    2,500                                    29     11,000     6,000     <600     <600                                     30     8,000      4,400     <600     <600                                     31     6,000      4,000     <600     <600                                     32     8,000      5,500     <600     <600                                     ______________________________________                                    

EXAMPLES 33 to 40

In order to investigate the thickening effect of the silica in a vinylester system, lacuna! are dispersed (toothed-disc dissolver with adiameter of 5 cm and a circumferential speed of 7.3 m/s) in a dissolver(commercially available under the name Dispermat F105, Getzmann,Reichshof-Heienbach, D) at room temperature for 15 min in 145.50 g of a40% by weight polyvinyl ester resin dissolved in styrene, having aviscosity of 500 mPa.s at 25° C. (commercially available under the namePalatal A430 from BASF AG, Ludwigshafen, D) and 4.50 g of silicaprepared in accordance with Examples 1 to 8. The viscosity of thecomposition is subsequently measured with a Brookfield viscometer RVTDV-II, spindle 6, at 25° C. The results are compiled in Table 3.

EXAMPLE 41

The procedure of Example 31 is repeated but employing, instead of asilica prepared as in Example 1, a pyrogenic silica which issurface-modified with dimethylsiloxy groups and has a carbon content of1.0% by weight and a specific surface area of 160 m² /g (measured by theBET method in accordance with DIN 66131 and 66132), and which can beprepared according to DE 42 21 716 (commercially available under thename WACKER HDK H20 from Wacker-Chemie GmbH, Munich,D). The results aregiven in Table 3.

EXAMPLE 42

The procedure of Example 31 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with trimethylsiloxy groups and has a carbon contentof 2.5% by weight and a specific surface area of 140 m² /g (measured bythe BET method in accordance with DIN 66131 and 66132), and which can beprepared according to DE 23 44 388 (commercially available under thename WACKER HDK H2000 from Wacker-Chemie GmbH, Munich, D). The resultsare given in Table 3.

EXAMPLE 43

The procedure of Example 9 is repeated but employing, instead of asilica prepared in accordance with Example 1, a pyrogenic silica whichis surface-modified with ammonium-functional organopolysiloxane and hasa carbon content of 5.5% by weight and a specific surface area of 110 m²/g (measured by the BET method in accordance with DIN 66131 and 66132),and which can be prepared according to DE-A 37 07 226 (commerciallyavailable under the name WACKER HDK H2050 EP from Wacker-Chemie GmbH,Munich, D). The measured results are given in Table 3.

EXAMPLE 44

The procedure of Example 9 is repeated but employing, instead of asilica prepared in accordance with Example 1, a hydrophilic pyrogenicsilica having a specific surface area of 200 m² /g (measured by the BETmethod in accordance with DIN 66131 and 66132), and which can beprepared according to DE 26 20 737 (commercially available under thename WACKER HDK N20 from Wacker-Chemie GmbH, Munich, D). The results aregiven in Table 3.

                  TABLE 3                                                         ______________________________________                                        Examples     Viscosity (mPa.s)                                                ______________________________________                                        33           4,400                                                            34           2,300                                                            35           4,500                                                            36           2,100                                                            37           5,900                                                            38           5,800                                                            39           2,200                                                            40           7,300                                                            41           3,000                                                            42           1,800                                                            43           1,900                                                            44           1,200                                                            ______________________________________                                    

Appendix I: Extractable silylating agent

25 g of silica are incorporated using a spatula into 100 g oftetrahydrofuran, and subsequently stirred together to a liquidconsistency with ice cooling and using a dissolver (Pentrauliklaboratory dissolver LD 50 with 40 mm toothed disc), and then sheared at8400 rpm for 60 sec and equilibrated with ultra-sound for 60 min, andafter 2 days a clear filtrate is filtered off by pressure filtration.The filtrate is investigated for its silicon content by atomicabsorption spectroscopy (AAS) and, after concentration by a factor of10, for its content of organosilicon compounds by gas chromatography(GC). Detection limit <100 ppm of organosilicon compounds, based onsilica.

Appendix ll: Relative sorption capacity for OH--

In accordance with Sears et al., Anal. Chem. 1956, 12, 1981, the contentof acidic silanol groups in the silica can be determined by titrationwith 0.1N sodium hydroxide solution in saturated sodium chloridesolution. If this method is applied to highly apolar silica, in generalthe sorption capacity for hydroxyl ions (OH--) is detected. The relativesorption capacity is then defined as "sorption capacity of the apolarsilica divided by the sorption capacity of the hydrophilic startingsilica, multiplied by 100".

Appendix III: Methanol number

Apolar silica, especially highly apolar silica, is by definition notwetted by water; this leads to the apolar silica floating on the waterbelow it, even after shaking. Addition of methanol to water lowers thesurface tension of the mixture relative to pure water. If the surfacetension (mN/m) of the water/methanol mixture is of equal magnitude tothe surface energy (mJ/m²) of the silica, the silica is wetted and sinksinto the water/methanol mixture. The methanol number is defined as thatpercentage (% by weight) of methanol in the water/methanol mixture atwhich half of the silica is wetted and sinks into the liquid. Procedure:Application of an equal volume of silica over the water/methanolmixture, intensive mixing by vigorous shaking for 5 min, then restingfor 10 min, followed by assessment of the quantity of silica which hassunk in.

Appendix IV: Thickening effect in UP resin

9 g of each silica are stirred into 141 g of a 66% strength by weightsolution of an unsaturated polyester resin in styrene, having an acidnumber in accordance with DIN 53402 of 31 and a viscosity at 23° C. of1000 mPa.s (commercially available under the name Ludopal P6 from BASF,Ludwigshafen, D) using a dissolver (Pentraulik laboratory dissolver LD50 with a 40 mm toothed disc) and are then dispersed at 2800 rpm. Theviscosity value at 25° C. measured with a rotary viscometer inaccordance with DIN 53019 Part 1 at a shear gradient of 9.7 cm⁻¹ isdefined as the "thickening effect in UP resin".

Appendix V: Thickening effect in 25% ethanol

15 g of each silica are pasted up in a mixture of 16.7 g of water and33.3 g of analytical-grade ethanol, then 85 g of water are added andstirred in with the dissolver (Pentraulik laboratory dissolver LD 50with a 40 mm toothed disc), and the mixture is then dispersed for 5 minat 2800 rpm. The viscosity value at 25° C. measured with a rotaryviscometer in accordance with DIN 53019 Part 1 at a shear gradient of9.7 cm⁻¹ is defined as the "thickening effect in 25% ethanol".

What is claimed is:
 1. Process for the silylation of very finely dividedinorganic oxides, wherein the very finely divided inorganic oxides aretreated with at least one silylating agent which is relativelynonvolatile in the temperature range of the overall process, with theproviso that the relatively nonvolatile silylating agent is admixed as aliquid with the very finely divided inorganic oxides, said liquid beingin the form of a very finely atomized aerosol.
 2. Process for thesilylation of very finely divided inorganic oxides according to claim 1,wherein the very finely divided inorganic oxides are additionallytreated with at least one silylating agent which is volatile at processtemperature, with the proviso that the volatile silylating agent isadmixed to the very finely divided inorganic oxides in gaseous form. 3.Process for the silylation of very finely divided inorganic oxidesaccording to claim 1, wherein the process comprises a first step ofmixing very finely divided inorganic oxides and silylating agent, asecond step of aftertreatment by heat treatment, and a third step ofpurification in a stream of gas.
 4. Process for the silylation of veryfinely divided inorganic oxides according to claim 1, wherein theprocess temperature is at temperatures below 400° C.
 5. Process for thesilylation of very finely divided inorganic oxides according to claim 1,wherein the silylating agent employed comprises one or moreorganosilicon compounds.
 6. Process for the silylation of very finelydivided inorganic oxides according to claim 1, wherein the very finelydivided inorganic oxide is additionally treated with a protic solvent.7. Process for the silylation of very finely divided inorganic oxidesaccording to claim 1, wherein the very finely divided inorganic oxidehas a carbon content of less than 1% by weight per 100 m² /g of specificsurface area.
 8. Process for the silylation of very finely dividedinorganic oxides according to claim 1, wherein the very finely dividedinorganic oxide used is silica.
 9. Process for the silylation of veryfinely divided inorganic oxides according to claim 1, wherein thesilylating agent comprises organosilanes of the formula

    R.sup.1.sub.n SiX.sub.4-n                                  (I)

in which R¹ is identical or different and is a monovalent, optionallyhalogenated, hydrocarbon radical having 1 to 18 carbon atoms, X isidentical or different and is a halogen, or OH, OR², OCOR², O(CH₂)_(x)OR², R² is identical or different and is a monovalent hydrocarbonradical having 1to 8 carbon atoms, n is 1, or 2, and x is 1, 2,3;organosiloxanes of the formula

    (R.sup.1.sub.a X.sub.b SiO.sub.1/2).sub.z (R.sup.1.sub.2 SiO.sub.2/2).sub.x (R.sup.3 R.sup.1 SiO.sub.2/2).sub.y (SiX.sub.b R.sup.1.sub.a).sub.z(II)

in which R¹ is as defined above, R² is as defined above R³ is identicalor different, and is a hydrogen or a monovalent, optionally halogenated,hydrocarbon radical having 1 to 18 carbon atoms which is different fromR¹, X is as defined above, a is 0, 1, 2 or 3, b is 0, 1,2or 3,the suma+b being equal to 3, x is 0 or an integer from 1 to 200, y is 0 or aninteger from 1 to 200,and the sum x+y being equal to 0 or an integerbetween 1 and 200, z is 0 or 1with the proviso that z is greater than 0if the sum x+y is equal to 0, and mixtures of formulae (I) and (II).